Actually we could create a triangle in this case. The hypotenuse is the radius of Earth plus the height above the earth, while the two sides are the radius of Earth and the scope of vision.
That is:
(6,400,000 m + 100 m)^2 = (6,400,000 m)^2 + b^2
b^2 = 1,280,010,000
b = 35,777.23 m
You can see 35,777.23 m far.